Solid-state imaging device driving method

ABSTRACT

Photosensitive cells each includes a photodiode ( 1 ), a transfer gate ( 2 ), a floating diffusion layer portion ( 3 ), an amplifying transistor ( 4 ), and a reset transistor ( 5 ). Drains of the amplifying transistors ( 4 ) of the photosensitive cells are connected to a power supply line ( 10 ), and a pulsed power supply voltage (VddC) is applied to the power supply line ( 10 ). Here, a low-level potential (VddC_L) of the power supply voltage has a predetermined potential higher than zero potential. Specifically, by making the low-level potential (VddC_L) higher than channel potentials obtained when a low level is applied to the reset transistors ( 5 ), or channel potentials obtained when a low level is applied to the transfer gates ( 2 ), or channel potentials of the photodiodes ( 1 ), a reproduced image with low noise is read.

TECHNICAL FIELD

The present invention relates to a method of driving a MOS-typesolid-state imaging device for use in various apparatuses such as homevideo cameras, digital still cameras, and mobile phone cameras.

BACKGROUND ART

With reference to FIGS. 5 and 6, a conventional sensor and a drivingmethod thereof will be described. FIG. 5 is a circuit diagram of aconventional sensor. The sensor shown in FIG. 5 has photosensitive cells(the portions surrounded by dotted-lines) arranged in a 2×2 matrix form.Each photosensitive cell includes a photodiode 51, a transfer gate 52, afloating diffusion layer portion 53, an amplifying transistor 54, areset transistor 55, and an address transistor 56, and corresponds toone of the pixels composing an image. Note that although the followingdescription will assume, for simplicity, that the photosensitive cellsare arranged in a 2×2 matrix form, in practice, several tens to severalthousands of photosensitive cells are arranged in each of the row andcolumn directions.

A method of driving the sensor shown in FIG. 5 is as follows. To extractsignals from photosensitive cells in the first row, first, addresstransistors 56 a and 56 b included in the photosensitive cells in thefirst row are controlled to be in an ON state by a vertical shiftregister 61. Then, reset transistors 55 a and 55 b are similarlycontrolled to be in an ON state by the vertical shift register 61. Thisresets floating diffusion layer portions 53 a and 53 b. At this stage,an amplifying transistor 54 a and a load transistor 63 p form a sourcefollower circuit, and an output from the source follower circuit appearson a vertical signal line 62 p. Similarly, an amplifying transistor 54 band a load transistor 63 q form a source follower circuit, and an outputfrom the source follower circuit appears on a vertical signal line 62 qas well. Voltages appearing on the vertical signal lines 62 p and 62 qat this stage are noise voltages which are unrelated to signal chargesaccumulated in photodiodes 51 a and 51 b. Subsequently, transfer gates52 a and 52 b are controlled to be in an ON state by the vertical shiftregister 61. By this, the signal charges accumulated in the photodiodes51 a and 51 b are transferred to the floating diffusion layer portions53 a and 53 b, and signal voltages corresponding to the signal chargesaccumulated in the photodiodes 51 a and 51 b appear on the verticalsignal lines 62 p and 62 q.

Clamp capacitors 64 p and 64 q, clamp transistors 65 p and 65 q,sample/hold transistors 66 p and 66 q, and sample/hold capacitors 67 pand 67 q form a noise suppression circuit. The noise suppression circuitdetermines the difference between a pixel output obtained when there aresignal charges in the floating diffusion layer portions 53 (i.e., asignal output) and a pixel output obtained when there is no signalcharge (i.e., a noise output). In the sensor shown in FIG. 5, mainly,noise caused by variations in the threshold voltages of the amplifyingtransistors 54 and kTC noise which is the thermal noise of the resettransistors 55 are generated. When noise outputs are appearing on thevertical signal lines 62 p and 62 q, the clamp transistors 65 p and 65 qand the sample/hold transistors 66 p and 66 q are controlled to be in anON state through control terminals 74 and 75, and a noise-free clampvoltage is applied to the sample/hold capacitors 67 p and 67 q from aclamp voltage supply terminal 73. After a predetermined time haselapsed, the clamp transistors 65 p and 65 q are controlled to be in anOFF state through the control terminal 74.

Subsequently, a voltage equal to the sum of a noise-free signal voltageand a noise voltage appears on each of the vertical signal lines 62 pand 62 q. The vertical signal lines 62 p and 62 q each change from thenoise voltage to the sum of the signal voltage and the noise voltage;the amount of the change is equal to the noise-free signal voltage.Therefore, the voltage of each of the clamp capacitors 64 p and 64 q onthe sample/hold side also changes by an amount equal to the noise-freesignal voltage. In practice, the voltage across each of the sample/holdcapacitors 67 p and 67 q changes from the noise-free clamp voltage by anamount obtained by dividing the amount of signal voltage change on thecorresponding vertical signal line 62 p or 62 q by a corresponding clampcapacitor and a corresponding sample/hold capacitor. Therefore, thevoltage across each of the sample/hold capacitors 67 p and 67 q is thenoise-free clamp voltage and the divided signal voltage, and the noiseportion is removed. After the sample/hold transistors 66 p and 66 q arecontrolled to be in an OFF state, horizontal transistors 68 p and 68 qare sequentially and selectively controlled to be in an ON state by ahorizontal shift register 69. By this, signals corresponding to thesignal charges accumulated in the photodiodes 51 a and 51 b aresequentially outputted from an output terminal 70.

Next, to extract signals from photosensitive cells in the second row,the same operations as for the first row are performed on thephotosensitive cells in the second row. By this, signals correspondingto signal charges accumulated in photodiodes 51 c and 51 d aresequentially outputted from the output terminal 70.

A timing chart showing the above-described operations is as shown inFIG. 6. In FIG. 6, the period during which signals accumulated inphotodiodes 51 for one row are finally outputted from the outputterminal 70 is called a horizontal effective period, and the periodduring which the signals are outputted from the photodiodes 51 to thevertical signal lines 62 and the noise of the outputted signals issuppressed is called a horizontal blanking period. The horizontalblanking period and the horizontal effective period are together calledone horizontal period. The one horizontal period is the time actuallyrequired to read signals for one row. The time required to read signalsfrom the entire sensor is called one frame period. As shown in FIG. 6,the amount of a signal charge accumulated in the photodiode 51 isdetermined by the time interval of a transfer pulse to be applied to thetransfer gate 52. The time interval of the transfer pulse is constantduring one frame period. Therefore, the photodiodes 51 have uniformsensitivity.

In the sensor shown in FIG. 5, each photosensitive cell is composed offour transistors (a transfer gate 52, an amplifying transistor 54, areset transistor 55, and an address transistor 56). On the other hand,in recent years, for reduction in size of sensors, there has developed asensor having photosensitive cells each composed of three transistors.This newly developed sensor has a configuration in which addresstransistors 56 are removed from the sensor shown in FIG. 5 and the powersupply is shared between the photosensitive cells. In order to readsignals from this sensor, it is necessary to supply a pulsed powersupply voltage to each photosensitive cell.

A method of driving the sensor shown in FIG. 5 is described in JapaneseLaid-Open Patent Publication No. 9-247537, for example. In addition,Japanese Laid-Open Patent Publication No. 2001-45375 describes a drivingmethod by which signals from photodiodes for one row are averagelyoutputted in one horizontal period.

However, in the sensor in which each photosensitive cell is composed ofthree transistors, because the power supply is pulse-driven, problemssuch as those described below may arise. First, since the power supplyis connected to all the photosensitive cells and not only a selectedphotosensitive cell but the entire sensor is driven, adverse effects areexerted on the operation of the entire sensor. Secondly, although thepower supply voltage at a high level does not exert adverse effects onthe operation of the sensor, the power supply voltage at a low levelexerts adverse effects on the operation of a non-selected photosensitivecell. Thirdly, pulse-driving of the power supply per se exerts variousadverse effects on the entire sensor.

In particular, in terms of the aforementioned second problem, if thelow-level potential of the power supply becomes too low, this low-levelpotential may become equal to or lower than the low-level potential ofthe reset transistors of non-selected photosensitive cells and reacheven to the gate regions of amplifying transistors. Here, a large numberof amplifying transistors simultaneously go into operation and drive theentire sensor. Accordingly, a great noise is superimposed during ahorizontal blanking period, and thereby signal processing becomesdifficult.

If the low-level potential of the power supply becomes equal to or lowerthan the low-level potential of the transfer gates of non-selectedphotosensitive cells, charges are injected into photodiodes, causingvariations in the amount of charge injected into the photosensitivecells. Accordingly, variations occur in signal charges to be read fromthe photodiodes and thereby a great noise appears in a reproduced image.

Therefore, an object of the present invention is to provide a method ofdriving a solid-state imaging device, by which a reproduced image withlow noise is read from a sensor having photosensitive cells eachcomposed of three transistors.

DISCLOSURE OF THE INVENTION

To achieve the above objects, the present invention has the followingaspects.

A first aspect of the present invention is directed to a method ofdriving a solid-state imaging device comprising: a photosensitive regionhaving photosensitive cells arranged two-dimensionally in row and columndirections on a semiconductor substrate, each photosensitive cellincluding a photodiode for accumulating a signal charge obtained byconverting incoming light into electricity; a transfer transistor fortransferring the signal charge accumulated in the photodiode; a floatingdiffusion layer portion for temporarily accumulating the transferredsignal charge; an amplifying transistor for amplifying the signal chargeaccumulated in the floating diffusion layer portion; and a resettransistor for resetting the signal charge accumulated in the floatingdiffusion layer portion; a power supply line commonly connected todrains of the amplifying transistors; a vertical driver circuit forindividually driving transfer transistors arranged in a same row andreset transistors arranged in the same row; a plurality of verticalsignal lines each having commonly connected thereto correspondingamplifying transistors arranged in a same column; a plurality of loadtransistors connected to the vertical signal lines, respectively; anoise suppression circuit for suppressing noise of signals outputted tothe vertical signal lines; a plurality of horizontal transistors whichare arranged in the row direction, and to which outputs from the noisesuppression circuit are inputted; and a horizontal driver circuit forallowing the horizontal transistors to sequentially and selectivelyoperate, and thereby sequentially outputting the outputs from the noisesuppression circuit, the method comprising the steps of: pulse-drivingthe power supply line on a per horizontal period basis; sequentiallyselecting different rows on a per horizontal period basis using thehorizontal driver circuit, and allowing corresponding reset transistorsand corresponding transfer transistors included in correspondingphotosensitive cells arranged in a selected row to successively operatewhile the power supply line is driven, and thereafter allowing thecorresponding reset transistors to operate while the power supply lineis not driven; and sequentially outputting outputs from the noisesuppression circuit on a per horizontal period basis using thehorizontal driver circuit, wherein a low-level potential of the powersupply line has a predetermined potential higher than zero potential.

According to the method of driving the solid-state imaging device, bymaking the low-level potential of the power supply line higher than zeropotential, it is possible to prevent the entire sensor from being drivenand to stabilize the potential of each pixel. Accordingly, a reproducedimage with low noise can be read.

In the method of driving the solid-state imaging device, thepredetermined potential may be higher than channel potentials obtainedwhen a low level is applied to the reset transistors. By doing so, theamplifying transistors are prevented from operating in the vicinity oftheir respective gate regions, and thus it is possible to prevent asituation where a large number of amplifying transistors simultaneouslygo into operation and as a result the entire sensor is driven.Accordingly, it is possible to solve a problem that a great noise issuperimposed during a horizontal blanking period, and thereby signalprocessing becomes difficult.

Alternatively, the predetermined potential may be higher than channelpotentials obtained when a low level is applied to the transfertransistors. By doing so, it is possible to prevent a situation wherebecause of the charges injected into the photodiodes, variations in theamount of charge to be injected occur in the photosensitive cells.Accordingly, a beautifully reproduced image with low noise can be readwithout causing a great noise to appear in the reproduced image.

Alternatively, the predetermined potential may be higher than channelpotentials of the photodiodes. By doing so, it is possible to preventthe entire sensor from being driven and to stabilize the potential ofeach pixel. Accordingly, a reproduced image with low noise can be read.

In the method of driving the solid-state imaging device, thephotosensitive region may be formed on a p-type substrate. By doing so,a reproduced image with low noise can be read from a solid-state imagingdevice having a photosensitive region formed on a p-type substrate.

Alternatively, the photosensitive region may be formed in a p-type wellon an n-type substrate. By doing so, a reproduced image with low noisecan be read from a solid-state imaging device having a photosensitiveregion formed in a p-type well on an n-type substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a sensor according to an embodiment ofthe present invention.

FIGS. 2A and 2B are diagrams showing the details of a noise suppressioncircuit of the sensor according to the embodiment of the presentinvention.

FIG. 3 is a timing chart showing a method of driving the sensoraccording to the embodiment of the present invention.

FIGS. 4A and 4B are a cross-sectional view and a potential diagram of aphotosensitive cell of the sensor according to the embodiment of thepresent invention.

FIG. 5 is a circuit diagram of a conventional sensor.

FIG. 6 is a timing chart showing a method of driving the conventionalsensor.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a circuit diagram of a sensor according to an embodiment ofthe present invention. The sensor shown in FIG. 1 has photosensitivecells (the portions surrounded by dotted-lines) arranged in an m×nmatrix form; a power supply line 10; a vertical shift register 11; nvertical signal lines 12-1 to 12-n; n load transistors 13-1 to 13-n; anoise suppression circuit 14; n horizontal transistors; and a horizontalshift register 16. Each photosensitive cell includes a photodiode 1, atransfer gate 2, a floating diffusion layer portion 3, an amplifyingtransistor 4, and a reset transistor 5. The photosensitive cell ischaracterized in that it includes three transistors (the transfer gate2, the amplifying transistor 4, and the reset transistor 5) and does notinclude an address transistor. The values of m and n in an actual sensorare in the order of from several tens to several thousands.

The m×n photosensitive cells are formed on a semiconductor substrate.More specifically, the photosensitive cells are formed on a p-typesubstrate or in a p-well on an n-type substrate. In each photosensitivecell, the photodiode 1 converts incoming light into electricity andaccumulates therein an obtained signal charge. The transfer gate 2 isprovided between the photodiode 1 and the floating diffusion layerportion 3, and transfers the signal charge accumulated in the photodiode1 to the floating diffusion layer portion 3. The floating diffusionlayer portion 3 temporarily accumulates therein the signal chargetransferred from the photodiode 1. The amplifying transistor 4 amplifiesthe signal charge accumulated in the floating diffusion layer portion 3.The reset transistor 5 resets the signal charge accumulated in thefloating diffusion layer portion 3.

In a photosensitive region where the photosensitive cells are arranged,pairs of m signals lines 17-1 to 17-m and 18-1 to 18-m are wired inaddition to the power supply line 10 and the vertical signal lines 12-1to 12-n. The power supply line 10 is commonly connected to drains of theamplifying transistors 4. The present embodiment assumes that the powersupply line 10 is commonly connected to the drains of the amplifyingtransistors 4 and the reset transistors 5 included in all thephotosensitive cells, and a pulsed power supply voltage VddC is appliedto all the photosensitive cells from a power supply terminal 20 which ispresent at the other end of the power supply line 10. Note thatalthough, in FIG. 1, all the photosensitive cells are connected to thesingle power supply line 10, two or more power supply lines may be usedto supply a common power supply to the photosensitive cells.

Each of the vertical signal lines 12-1 to 12-n is provided to acorresponding column of photosensitive cells. The vertical signal lines12-1 to 12-n connect between corresponding amplifying transistors 4included in photosensitive cells and corresponding load transistors 13-1to 13-n, which are arranged in the same column, and the noisesuppression circuit 14. The signal lines 17-1 to 17-m and 18-1 to 18-mare output signal lines of the vertical shift register 11, and are eachprovided to a corresponding row of photosensitive cells. The signallines 17-1 to 17-m connect between gates of corresponding transfer gates2 included in photosensitive cells arranged in the same row. The signallines 18-1 to 18-m connect between gates of corresponding resettransistors 5 included in photosensitive cells arranged in the same row.

The vertical shift register 11 operates as a vertical driver circuit asdescribed below. When the power supply line VddC is at a high level, thevertical shift register 11 simultaneously drives corresponding transfergates 2 included in photosensitive cells arranged in the same row. Inaddition, when the power supply line VddC is at a high level, thevertical shift register 11 simultaneously drives corresponding resettransistors 5 included in photosensitive cells arranged in the same row,at a different timing than the drive timing of the transfer gates 2. Theload transistors 13-1 to 13-n are connected to the vertical signal lines12-1 to 12-n, respectively, and arranged in the row direction. The noisesuppression circuit 14 is connected to the vertical signal lines 12-1 to12-n, and captures signals outputted from the amplifying transistors 4and then removes the noise component in the captured signals. Horizontaltransistors 15-1 to 15-n are arranged in the row direction. To thehorizontal transistors 15-1 to 15-n are inputted n signals outputtedfrom the noise suppression circuit 14, respectively. The horizontalshift register 16 operates as a horizontal driver circuit. Specifically,the horizontal shift register 16 allows the horizontal transistors 15-1to 15-n to sequentially and selectively operate. By doing so, the nsignals outputted from the noise suppression circuit 14 are sequentiallyoutputted from the output terminal 21.

FIGS. 2A and 2B are diagrams for describing the details of the noisesuppression circuit 14. The noise suppression circuit 14 includes, asshown in FIGS. 2A, n sample/hold transistors 31-1 to 31-n; n clampcapacitors 32-1 to 32-n; n clamp transistors 33-1 to 33-n; and nsample/hold capacitors 34-1 to 34-n. The noise suppression circuit 14 isdifferent from the noise suppression circuit shown in FIG. 5 in theposition of the sample/hold transistors 31-1 to 31-n, but operatessubstantially in the same manner as the noise suppression circuit shownin FIG. 5. A sample/hold control signal inputted from a control terminal22 is applied to gates of the sample/hold transistors 31-1 to 31-n.Similarly, a clamp control signal inputted from a control terminal 23 isapplied to gates of the clamp transistors 33-1 to 33-n. These twocontrol signals change as shown in FIG. 2B. A period during which bothof the two control signals are at a high level serves as a noise outputperiod, and a period during which the sample/hold control signal is at ahigh level and the clamp control signal is at a low level serves as asignal output period.

With reference to a timing chart shown in FIG. 3, where appropriate, amethod of driving the sensor shown in FIG. 1 will be described below. Todrive the sensor, there are performed a step of pulse-driving the powersupply line 10 on a per horizontal period basis; a step of readingsignals for one row from the m×n photodiodes 1 using the vertical shiftregister 11; and a step of sequentially outputting the read signals forone row using the horizontal shift register 16.

As shown in FIG. 3, in an initial state, a power supply voltage VddC isat a low level. That is, in the initial state, the power supply line 10is not yet driven. To extract signals from the photosensitive cells inthe first row, first, the power supply voltage VddC is controlled to beat a high level. By this, in all the photosensitive cells, the drains ofthe transfer gates 2 and the reset transistors 5 are brought to a highlevel. Then, while the power supply line 10 is driven, the verticalshift register 11 brings the signal line 18-1 to a high level for apredetermined period of time. By this, the gate potentials of the resettransistors 5 a and 5 b and all other reset transistors 5 included inthe photosensitive cells in the first row are brought to a high level,and these reset transistors 5 are brought into an ON state. At thisstage, the amplifying transistors 4 a and 4 b and all other amplifyingtransistors 4 included in the photosensitive cells in the first row arebrought into an operation state. At the same time, noise outputs, whichare generated when signal charges accumulated in the floating diffusionlayer portions 3 a and 3 b and all other floating diffusion layerportions 3 included in the photosensitive cells in the first row arereset, appear on the vertical signal lines 12-1 to 12-n.

Subsequently, while the power supply line 10 is driven, the verticalshift register 11 brings the signal line 17-1 to a high level for apredetermined period of time. By this, the gate potentials of thetransfer gates 2 a and 2 b and all other transfer gates 2 included inthe photosensitive cells in the first row are brought to a high level,and these transfer gates 2 are brought into an ON state. At this stage,signal charges accumulated in the photodiodes 1 a and 1 b and all otherphotodiodes 1 included in the photosensitive cells in the first row areread into corresponding floating diffusion layer portions 3 included inthe photosensitive cells, and then signal outputs corresponding to theread signal charges appear on the vertical signal lines 12-1 to 12-n.

In this manner, on each of the vertical signal lines 12-1 to 12-n, aftera noise voltage appears, the sum of a signal voltage and the noisevoltage appears. The noise suppression circuit 14 operates in the samemanner as the conventional noise suppression circuit, and suppresses thenoise of the signals outputted to the vertical signal lines 12-1 to12-n. The n signals outputted from the noise suppression circuit 14 areinputted to the horizontal transistors 15-1 to 15-n, respectively.

After the noise suppression circuit 14 goes into operation, the powersupply voltage VddC changes to a low level. Then, while the power supplyline 10 is not driven, the vertical shift register 11 brings the signalline 18-1 to a high level for a predetermined period of time. By this,signal charges accumulated in the floating diffusion layer portions 3 aand 3 b and all other floating diffusion layer portions 3 included inthe photosensitive cells in the first row are reset. The amplifyingtransistors 4 a and 4 b and all other amplifying transistors 4 includedin the photosensitive cells in the first row remain in a non-operationstate until they are selected again.

The horizontal shift register 16 outputs n output signals connected tothe gates of the horizontal transistors 15-1 to 15-n. The horizontalshift register 16 selectively brings the n output signals to a highlevel, and thereby sequentially and selectively controls the horizontaltransistors 15-1 to 15-n to be in an ON state. By this, signalscorresponding to the signal charges accumulated in the photodiodes 1 aand 1 b and all other photodiodes 1 in the first row are sequentiallyoutputted from the output terminal 21.

Then, to extract signals from the photosensitive cells in the secondrow, the same operations as for the fist row are performed on thephotosensitive cells in the second row. By this, signals correspondingto signal charges accumulated in the photodiodes 1 c and 1 d and allother photosensitive cells in the second row are sequentially outputtedfrom the output terminal 21. Thereafter, the same operations areperformed on photosensitive cells from the third to the m-th rows. Notethat the definitions of a horizontal blanking period, a horizontaleffective period, one horizontal period, and one frame period shown inFIG. 3 and the fact that the photodiodes 1 have uniform sensitivity, arethe same as those for the conventional sensor.

Of methods of driving a sensor, such as that described above, thepresent embodiment considers a driving method which is characterized inthat the low-level potential of a power supply voltage VddC is apredetermined potential higher than zero potential. Specifically, thereare considered a driving method in which the low-level potential of thepower supply voltage VddC is higher than the channel potentials obtainedwhen a low level is applied to reset transistors 5, and a driving methodin which the low-level potential of the power supply voltage VddC ishigher than the channel potentials obtained when a low level is appliedto transfer gates 2. According to the driving methods having suchcharacteristics, a reproduced image having less noise than that obtainedby conventional driving methods can be obtained. The reasons will bedescribed below with reference to FIGS. 4A and 4B.

FIGS. 4A and 4B are respectively a cross-sectional view and a potentialdiagram of a photosensitive cell included in the sensor shown in FIG. 1.In FIG. 4A, the photosensitive cell is formed on a p-type substrate. Thep-type substrate, an n-type photodiode layer 41 formed on the p-typesubstrate, and a p-type surface layer 42 formed on a surface of thep-type substrate, compose a photodiode 1. In addition to the photodiode1, a floating diffusion layer portion 3 and an n-type surface layer 45are formed on the p-type substrate. Upon this, by providing an electrode43 a transfer gate 2 is formed, and by providing an electrode 44 a resettransistor 5 is formed.

As described above, the power supply voltage VddC changes in pulse form.Here, the high-level potential and low-level potential of the powersupply voltage VddC are noted as VddC_H and VddC_L, respectively (seeFIG. 4B). The actual value of VddC_H is 2.8 V, for example. A voltagewhich varies within a range from 0 V to 2.8 V is applied to the gates ofthe reset transistors 5; the channel potentials obtained when alow-level potential (0 V) is applied to the gates of the resettransistors 5 are noted as TRchL. A voltage which varies in a range from0 V to 2.8 V is also applied to the gates of the transfer gates 2; thechannel potentials obtained when a low-level potential (0 V) is appliedto the gates of the transfer gates 2 are noted as TRchL. With the use ofthe notation, in the present embodiment, the low-level potential VddC_Lof the power supply voltage is controlled such that the followingrelationship(s) holds:RSchL<VddC_L   (1)and/orTRchL<VddC_L   (2).

The use of a low-level potential VddC_L for which the aforementionedexpression (1) holds, prevents the amplifying transistors 4 fromoperating in the vicinity of their respective gate regions. Thus, aphenomenon does not occur in which a large number of amplifyingtransistors 4 simultaneously go into operation and as a result theentire sensor is driven. Accordingly, it is possible to solve a problemthat a great noise is superimposed during a horizontal blanking period,and thereby signal processing becomes difficult.

The use of a low-level potential VddC_L for which the aforementionedexpression (2) holds, prevents a phenomenon from occurring in whichbecause of the charges injected into the photodiodes 1 variations in theamount of charge to be injected occur in the photosensitive cells.Accordingly, it is possible to read a beautifully reproduced imagewithout causing a great noise to appear in the reproduced image.

As described above, by using a low-level potential VddC_L of the powersupply voltage for which the aforementioned expression(s) (1) and/or (2)holds, the entire sensor is not driven and the potential of each pixelis stabilized, and therefore it is possible to read a beautifullyreproduced image with low noise.

Note that, in practice, in place of the aforementioned expressions (1)and (2), or in addition to the aforementioned expression(s) (1) and/or(2), as the low-level potential VddC_L of the power supply voltage, apotential higher than the channel potentials of photodiodes may be used.In the case of using such a potential, a reproduced image with low noisecan be read from the sensor shown in FIG. 1 as well.

For a sensor to which the driving method according to the presentembodiment is applicable, a sensor formed on a p-type substrate, asshown in FIG. 4A, may be used or a sensor formed on a p-well in ann-type substrate may be used. The driving method according to thepresent embodiment is applicable to a sensor formed by either method.

INDUSTRIAL APPLICABILITY

As described above, the method of driving a solid-state imaging deviceaccording to the present invention has characteristics in that areproduced image with low noise can be read, and thus can be used as adriving method by which a reproduced image is read from varioussolid-state imaging devices.

1. A method of driving a solid-state imaging device comprising: a photosensitive region having photosensitive cells arranged two-dimensionally in row and column directions on a semiconductor substrate, each photosensitive cell including a photodiode for accumulating a signal charge obtained by converting incoming light into electricity; a transfer transistor for transferring the signal charge accumulated in the photodiode; a floating diffusion layer portion for temporarily accumulating the transferred signal charge; an amplifying transistor for amplifying the signal charge accumulated in the floating diffusion layer portion; and a reset transistor for resetting the signal charge accumulated in the floating diffusion layer portion; a power supply line commonly connected to drains of the amplifying transistors; a vertical driver circuit for individually driving transfer transistors arranged in a same row and reset transistors arranged in the same row; a plurality of vertical signal lines each having commonly connected thereto corresponding amplifying transistors arranged in a same column; a plurality of load transistors connected to the vertical signal lines, respectively; a noise suppression circuit for suppressing noise of signals outputted to the vertical signal lines; a plurality of horizontal transistors which are arranged in the row direction, and to which outputs from the noise suppression circuit are inputted; and a horizontal driver circuit for allowing the horizontal transistors to sequentially and selectively operate, and thereby sequentially outputting the outputs from the noise suppression circuit, the method comprising the steps of: pulse-driving the power supply line on a per horizontal period basis; sequentially selecting different rows on a per horizontal period basis using the horizontal driver circuit, and allowing corresponding reset transistors and corresponding transfer transistors included in corresponding photosensitive cells arranged in a selected row to successively operate while the power supply line is driven, and thereafter allowing the corresponding reset transistors to operate while the power supply line is not driven; and sequentially outputting outputs from the noise suppression circuit on a per horizontal period basis using the horizontal driver circuit, wherein a low-level potential of the power supply line has a predetermined potential higher than zero potential.
 2. The method of driving the solid-state imaging device according to claim 1, wherein the predetermined potential is higher than channel potentials obtained when a low level is applied to the reset transistors.
 3. The method of driving the solid-state imaging device according to claim 1, wherein the predetermined potential is higher than channel potentials obtained when a low level is applied to the transfer transistors.
 4. The method of driving the solid-state imaging device according to claim 1, wherein the predetermined potential is higher than channel potentials of the photodiodes.
 5. The method of driving the solid-state imaging device according to claim 1, wherein the photosensitive region is formed on a p-type substrate.
 6. The method of driving the solid-state imaging device according to claim 1, wherein the photosensitive region is formed in a p-type well on an n-type substrate. 